1. Field of the Invention
The present invention relates to a plasma processing apparatus, and more particularly to a plasma processing apparatus including a mechanism for cleaning the outer edge of the backside of a specimen.
2. Description of the Related Art
In a process for manufacturing a semiconductor device, such as a DRAM or a microprocessor, plasma etching, plasma CVD, and plasma ashing utilizing a weakly ionized plasma are widely used. To improve the yield in the manufacturing process of the semiconductor device, it is important to reduce particles adhering to the specimen during the plasma processing.
In recent years, as semiconductor devices have been downsized, processing gases that tend to build up a deposition layer on a specimen have been used more frequently. However, the use of such processing gases generates a deposited film on the outer edge of the backside of the specimen in the plasma processing. The deposited film may peel off to become matters adhering to the specimen, for example, during the transfer of the specimen.
FIG. 12 illustrates a mechanism by which deposits are formed on the outer edge of the backside of the specimen 2 on a mounting electrode 4. The specimen 2 is mounted on a specimen-mounting face of the mounting electrode 4 such that about 1 to 2 mm of the edge of the specimen 2 extends past the edge of the mounting electrode 4. This prevents the wearing out of the top face of the mounting electrode 4 due to the impact of incident plasma particles. In other words, because ions 32 generated in plasma 15 collide with the specimen 2 at right angles, the ions 32 can hardly collide with the edge of the backside of the specimen 2 that extends past the mounting electrode 4, that is, a portion hidden behind the specimen 2 from the plasma 15.
However, neutral particles 33 in the plasma 15 collide with the specimen 2 and a focus ring 12 at different angles. Some of the neutral particles bounced off the specimen 2 and the mounting electrode 4 finally collide with the portion hidden behind the specimen 2 from the plasma 15. Thus, the neutral particles, which tend to build up on the specimen 2, adhere to the outer edge of the backside of the specimen 2. The adhering neutral particles are not removed by incident ions and thus grow into a thick deposited film 34.
Methods for removing the deposited film on the outer edge of the backside of the specimen and measures for preventing the formation of the deposited film have been proposed. For example, Japanese Unexamined Patent Application Publication No. 2004-200353 discloses a method for preventing the formation of a deposited film around a substrate specimen. This method comprises feeding a gas that reacts with and thereby eliminates the deposited film into the periphery of the back side of the substrate specimen.
Japanese Unexamined Patent Application Publication No. 2004-200219 also discloses a method for preventing the formation of a deposited film on the outer edge of a specimen. This method comprises performing plasma processing while the outer edge of the specimen is protected with a cover. Japanese Unexamined Patent Application Publication No. 9-283459 discloses a method for removing a deposited film on the backside of a specimen. This method comprises generating cleaning plasma between a mounting electrode and the specimen while the specimen is raised from the mounting electrode.
In the method according to the Japanese Unexamined Patent Application Publication No. 2004-200353, the gas that eliminates the deposited film diffuses into a processing chamber and may cause deterioration of a film on the specimen or erosion of a micropattern. In the method according to the Japanese Unexamined Patent Application Publication No. 9-283459, the plasma wears a specimen-mounting face of the mounting electrode. In the method according to the Japanese Unexamined Patent Application Publication No. 2004-200219, an electric field around the outer edge of the specimen may be distorted in a manner that depends on the geometry of the protective cover. The distorted electric field changes incident angles of ions and causes the deformation of a finished shape of the outer edge of the specimen, for example, in an etching apparatus. Thus, it is not always desirable to put the protective cover on the outer edge of the specimen during the plasma processing.
Considering these problems, the present invention provides a plasma processing apparatus that can efficiently remove a deposited film on the outer edge of the backside of a specimen.
The present invention employs the following means to solve the problems described above.